The process and apparatus of the present invention, as well as that of the copending application heretofore mentioned, have been found very useful in that they represent an efficient, inexpensive and satisfactory system for skinning tuna fish. Further, as will be apparent below, the present invention is also a meaningful improvement over the aforementioned copending application.
These inventions are in sharp contrast to the many types of commercial fish skinner equipment and systems that have been used heretofore which comprise various combinations of abrasive or cutting devices. Other systems use chemical penetration and peeling to disintegrate and loosen the skin to remove the skins. These methods are complicated and expensive. Many of them do not work satisfactorily on tuna fish because they are harmful to the skin and the meat thereunder and cause disintegration of the tuna meat.
Attempts have been made to also remove the tuna skin with a frozen roller, a tomato disk scrubber, by microwave application, a modified tomato steam peeler, conforming diaphragms and various types of fish de-skinning equipment and high-pressure waterjet spraying means.
The foregoing systems are not satisfactory because they either do not remove enough skin, or remove excessive meat. The problem with de-skinner equipment and processes used prior to our copending application is that such de-skinners were designed to work on fresh fish. They do not work satisfactorily on frozen, or frozen and precooked fish such as tuna fish, because the processed fish de-skins differently from fresh fish.
The machine of my copending application, though useful and advantageous, is capable of removing the skin from only one side of the fish when it passes through the machine. Thus, although useful, particularly with large size fish, it does require the extra step of manually turning over the fish and refeeding it through the machine so that the other side of the fish can be treated. In the final analysis it is clear that there is a need for a new process and machine for de-skinning tuna capable of reducing processing labor while removing a minimum of 80% of the skin with a light meat yield loss of less than 1% of the weight of the frozen fish. This is in contrast to the prior art methods mentioned above wherein high pressure waterjet spraying removed less than half the skin with fresh loss in the range of 2-10% of the weight of the fish.
With the present invention it has been possible to remove a minimum of 80% skin from a fragile cooked and cooled fish with less than one percent flesh loss, as will be described hereinafter. The fish to be treated are supported on a conveyor belt while being brushed with a combination of overhead and side brushes. Such brushes are of a different construction and are run at different speeds to conform to the de-skinning needs. At the same time a small amount of water is used to help keep the belt and brushes clean and to aid skin removal. Meanwhile a wheel and belt arrangement are used to gently turn over the fish to expose the opposite side for de-skinning and similar treatment with brushes and water sprays. The machine uses simple paddle-type brushes that brush over the precooked and cooled fish and gently remove skin without removing an excess of flesh. The fish being treated is thus being conveyed and supported on a belt-type surface while passing through the brushes. As heretofore stated, the great advantage of the machine is that a fish can be treated on both sides and the back and belly thereof can be de-skinned without manually turning the fish during the operation. This cleaning is effected by the brushes which may be mounted in a fixed or solid manner, or made moveable, to compensate for a changing fish shape. The brushes can also be operated to rotate with or against the direction of fish travel, and likewise the fish can be fed head-end or tail-end first. It is preferred to design and mount the brushes so that they rotate in the direction of fish travel, to thus enable the brushes to aid the fish through the machine. Nevertheless, the machine can be operated to de-skin a fish effectively with the brushes rotating opposite to the direction of travel of the fish.
As above-stated, de-skinning of one side and at least a portion of the back and belly of the fish when completed enables the fish to be turned over so that the bottom side, and optionally the back and belly, are exposed for completion of brushing. Such turn over of the fish can be effected in two ways. One is by passing the fish over a turn over wheel as discussed hereinafter, and the other is by sliding the fish down a spiral chute and arranging delivery of the fish so that it is turned over upon delivery from the end of the chute. The turn over wheel method is preferred because it gently turns the fish without disturbing the orientation or spacing thereof, and with no detectable damage to the fish.
The side brushes of the machine can be operated in a variety of ways that enable the skin to be removed from the belly and back in pairs so that both are brushed simultaneously or one brush can be opposed with a live surface belt or a sliding surface. A preferred method is to use two opposed spring loaded brushes each running at a different speed. The brush used to skin the back is generally run at a greater speed than the brush used to de-skin the belly. Because of the nature of the tuna fish, the more aggressive brushing by the high speed brush is desirable to remove the back skin in contrast to the belly skin. The speed of each brush can be optimized and adjusted to the rate that is most satisfactory for the task at hand. It is to be further noted that the fish can be arranged in a single lane, on a somewhat narrow belt, or for quantity treatment and greater efficiency, a wider belt can be employed and an additional line or lines of fish can be placed thereon for treatment in the machine. FIGS. 6 and 7, respectively, show mounting arrangements for the substantially vertical edge brushes, and the substantially horizontal side brushes. FIG. 4 shows the preferred arrangement of the brushes when finally assembled, as will be explained hereinafter.
Efficiency in removal of skin from each fish is substantially enhanced by spraying water directly on the bristles of the brushes. Preferably, the spray is directed against the bristles just before they contact the skin surface to be removed. Such a spray assures that any debris that sticks to the bristles during a previous revolution of the brush is washed away and that the scraping or abrading action on the skin is always in the presence of water. The spray also assures that the surface of the conveyor belt is sufficiently wet to discourage abraded debris, from previously skinned fish, from sticking to the upper conveying surface. Further, the surface of an already de-skinned fish is preferably kept wet enough by water from such spray to prevent deposit of debris from other fish being cleaned simultaneously from sticking to its cleaned surface.